In the past, rubber which contains α,β-ethylenically unsaturated nitrile monomer units and conjugated diene monomer units or olefin monomer units (nitrile copolymer rubber) has been known as rubber which is excellent in oil resistance. Its cross-linked product is mainly used as material for rubber products around oils in automotive applications such as hoses for fuel use, gaskets, packings, and oil seals.
On the other hand, in recent years, due to rising global activities to protect the environment, efforts are being made to reduce the amount of evaporation of gasoline and other fuel into the atmosphere. In Japan as well, in applications for fuel hoses, seals, and packings, much better gasoline permeation resistance is being sought in addition to mechanical properties such as tensile strength.
In this situation, Patent Document 1 discloses, as a nitrile copolymer rubber composition which gives a cross-linked product which is improved in gasoline permeation resistance, a nitrile copolymer rubber composition which contains a nitrile copolymer rubber which has 10 to 65 wt % of α,β-ethylenically unsaturated nitrile monomer units, 15 to 89.9 wt % of conjugated diene units, and 0.1 to 20 wt % of cationic monomer units and/or monomer units able to form cations and a flat-shaped inorganic filler with an aspect ratio of 30 to 2,000.
However, in the art of the above Patent Document 1, while the gasoline permeation resistance and cold resistance are improved to a certain degree, due to the higher degree of properties demanded in recent years, further improvement of the gasoline permeation resistance and cold resistance have been sought.